When a number of terminals access at least one slave computer using a communications system, as for example, a Local Area Network (LAN) having a communications protocol, total message traffic on the LAN may grow to exceed the capacity of the LAN. Total message traffic on the LAN may be particularly heavy when the terminals are small computers capable of up-loading files to the slave, and also when the terminals are capable of supporting a windows protocol. For example, a "mouse" input device is usually supported by a windows protocol, and motion of the mouse may generate a large number of messages to the slave (host) containing mouse position information. Also, in a windows protocol a terminal occasionally must transfer large amounts of data, for example the values of each pixel in the screen display, to the slave computer. In any event, the LAN may be overwhelmed by the amount of data being transferred from the terminal to the slave computer.
Communications protocols frequently require that each message sent from the terminal be acknowledged by the slave. The acknowledgment requirement is instituted in order to keep track of messages which are corrupted by noise on the communications circuits, or otherwise lost. A protocol having a terminal server as a master and a host computer as a slave is disclosed in U.S. Pat. No. 4,975,905, "Message Transmission Control Arrangement for Node in Local Area Network", issued Dec. 4, 1990, to Mann, Duffy, Lauck, and Strecker, and this protocol requires an acknowledgment by the slave to the master.
As a consequence of the acknowledgment requirement, each message from the terminal to the slave generates an acknowledgment message, and additionally usually generates one or more further response messages created by the slave in response to processing the received message. Congestion on the LAN therefore arises not only from the messages sent by the master to the slave computer, but also from the acknowledgment traffic sent from the slave to the master.
Delayed acknowledgment protocols have been used in the past in order to reduce ACK traffic on a local area network. However, a traditional implementation of delayed acknowledgment, as for example described in the textbook "Computer Networks" Second Edition, by A. S. Tanenbaum, published by Prentice Hall, Englewood Cliffs, N.J., in 1988, at Section 4.4 "Sliding Windows Protocol", pages 233-239, will not work optimally with a master--slave protocol.
It is desirable for the slave computer to both acknowledge the receipt of message packets from the master, and to reduce the number of messages carried by the local area network.